Phones (or telephones) are objects seen commonly in the Office. Almost all employees, including Stanley himself, have a telephone on their working desks or rooms.
There is a phone located on desk 434, which is just outside Stanley's Office, where Stanley may receive three random calls from either his wife, a Future Happiness Foundation employee, or a random stranger. Answering the call from the Future Happiness Foundation will make the office full with cardboard boxes upon beginning the game again.
A phone also serves as a Point of Divergence. After Stanley rides the cargo lift in the Warehouse, he is lead into the Phone Room where a phone presents. If Stanley picks it up, he will be taken into the Phone Ending. But if he decides to unplug the phone, he will end up in the Not Stanley Ending.